Wireless circuitry with reduced harmonic interference

ABSTRACT

An electronic device has wireless communications circuitry that includes transmitters and receivers. Antenna structures may be coupled to the transmitters and receivers to support radio-frequency signal transmission and radio-frequency signal reception operations. Switching circuitry such as first and second radio-frequency switches may be used to support multiple communications bands of interest. A low band set of transmitters may be associated with the first switch and a high band set of transmitters may be associated with the second switch. The switches can be configured in real time to switch a desired communications band into use. As transmitted signals at frequency f pass through the switches, harmonics at 2f, 3f, and other integral multiples of the transmitted signals may be produced. A diplexer may be interposed between the switching circuitry and the antenna structures that prevents the harmonics from reaching the antenna structures.

This application claims the benefit of provisional patent applicationNo. 61/363,485, filed Jul. 12, 2010, which is hereby incorporated byreference herein in its entirety.

BACKGROUND

This relates generally to wireless communications circuitry, and moreparticularly, to circuitry in wireless electronic devices that reducesinterference from frequency harmonics.

Electronic devices such as computers and cellular telephones are oftenprovided with wireless communications capabilities. For example,electronic devices may use long-range wireless communications circuitrysuch as cellular telephone circuitry. Global Positioning System (GPS)receiver circuitry and other satellite receiver circuitry may be used toreceive satellite navigation signals. Local wireless links may be usedto support local area network communications such as IEEE 802.11communications at 2.4 GHz and 5 GHz. Local links may also be used tohandle Bluetooth® communications at 2.4 GHz.

It is often desirable for a device to support multiple bands. Forexample, users of a cellular telephone may desire to communicate withcellular telephone towers using one or more different cellular telephonebands and may desire to communicate with local area network equipmentusing wireless local area network (WLAN) communications bands.

When supporting multiple bands, it is sometimes desirable to useconfigurable switching circuitry to route signals. In a device having atransceiver with numerous transceiver ports, for example, a switch maybe used to selectively couple a selected one of the transceiver ports toan antenna. This type of configuration allows the device to beconfigured in different ways, depending on the desired band ofoperation. If, for example, it is desired to use a first communicationsband, the switch may be placed in a first state that couples a firsttransceiver port to the antenna. When it is desired to use a secondcommunications band, the switch may be placed in a second state thatcouples a second transceiver port to the antenna.

Radio-frequency switches may be based on components such as transistorsthat exhibit non-linear behavior. As a result, undesired frequencyharmonics may be generated when radio-frequency signals are transmittedthrough a switch. For example, second harmonics, third harmonics, andhigher-order harmonics of transmitted radio-frequency signals may begenerated. If care is not taken, these harmonic signals may interferewith the operation of receiver circuitry in the device. For example,harmonics that are generated during transmission of cellular telephonesignals may interfere with proper operation of a satellite navigationreceiver or wireless local area network receiver.

It would therefore be desirable to be able provide improved circuitryfor routing signals between radio-frequency transceiver ports andantenna structures in a wireless electronic device.

SUMMARY

An electronic device may be provided with wireless communicationscircuitry. The wireless communications circuitry may includeradio-frequency transceiver circuitry for handling wirelesscommunications. The radio-frequency transceiver may have multipletransmitters and multiple receivers. Antenna structures may be used totransmit and receive signals.

The antenna structures may be coupled to transmitters and receivers inthe radio-frequency transceiver circuitry. Switching circuitry such asfirst and second radio-frequency switches may be used to supportmultiple communications bands of interest. The first and secondradio-frequency switches may be configured in real time to switchdesired frequencies into use.

A set of low band transmitters and receivers may be associated with thefirst switch and a set of high band transmitters and receivers may beassociated with the second switch. As transmitted signals at frequency fpass through the switches, harmonics at 2f, 3f, and other integralmultiples of the transmitted signals may be produced.

A diplexer may be interposed between the first and second switches andthe antenna structures. The diplexer may have a first port that iscoupled to the first radio-frequency switch, a second port that iscoupled to the second radio-frequency switch, and a third port that iscoupled to one or more antennas in the antenna structures.

The diplexer may include a low band filter associated with the low bandtransmitters and receivers and a high band filter associated with thehigh band transmitters and receivers. The low band filter may be a lowpass filter that is coupled between the first switch and the antennastructures. The low pass filter may prevent transmitted signal harmonicsthat exit the first switch from reaching the antenna structures. Thediplexer may include high band and low band filters that exhibit highdegrees of linearity such as filters implemented on ceramic substrates.Highly linear filters such as filters with ceramic substrates may have areduced tendency to produce undesired harmonics relative to other filterdesigns.

The high band filter may be a high pass filter or a band pass filter.When implemented using a bandpass filter, the high band filter mayprevent transmitted signal harmonics that exit the second switch fromreaching the antenna structures.

Further features of the invention, its nature and various advantageswill be more apparent from the accompanying drawings and the followingdetailed description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an illustrative electronic device withwireless communications circuitry in accordance with an embodiment ofthe present invention.

FIG. 2 is a diagram showing how radio-frequency transceiver circuitrymay be coupled to one or more antennas within an electronic device ofthe type shown in FIG. 1 in accordance with an embodiment of the presentinvention.

FIG. 3 is a circuit diagram of illustrative wireless communicationscircuitry of the type that may be used in handling wirelesscommunications in the electronic device of FIG. 1 in accordance with anembodiment of the present invention.

FIG. 4 is a graph of radio-frequency signal transmission as a functionof operating frequency for an illustrative low band filter that may beused in a diplexer within the wireless circuitry of FIG. 3 in accordancewith an embodiment of the present invention.

FIG. 5 is a graph of radio-frequency signal transmission as a functionof operating frequency for an illustrative high band filter that may beused in a diplexer within the wireless circuitry of FIG. 3 in accordancewith an embodiment of the present invention.

DETAILED DESCRIPTION

Electronic devices such as device 10 of FIG. 1 may be provided withwireless communications circuitry. The wireless communications circuitrymay be used to support long-range wireless communications such ascommunications in cellular telephone bands. Examples of long-range(cellular telephone) bands that may be handled by device 10 include the800 MHz band, the 850 MHz band, the 900 MHz band, the 1800 MHz band, the1900 MHz band, the 2100 MHz band, the 700 MHz band, and other bands. Thelong-range bands used by device 10 may include the so-called LTE (LongTerm Evolution) bands. The LTE bands are numbered (e.g., 1, 2, 3, etc.)and are sometimes referred to as E-UTRA operating bands. Long-rangesignals such as signals associated with satellite navigation bands maybe received by the wireless communications circuitry of device 10. Forexample, device 10 may use wireless circuitry to receive signals in the1575 MHz band associated with Global Positioning System (GPS)communications. Short-range wireless communications may also besupported by the wireless circuitry of device 10. For example, device 10may include wireless circuitry for handling local area network linkssuch as WiFi® links at 2.4 GHz and 5 GHz, Bluetooth® links at 2.4 GHz,etc.

As shown in FIG. 1, device 10 may include storage and processingcircuitry 28. Storage and processing circuitry 28 may include storagesuch as hard disk drive storage, nonvolatile memory (e.g., flash memoryor other electrically-programmable-read-only memory configured to form asolid state drive), volatile memory (e.g., static or dynamicrandom-access-memory), etc. Processing circuitry in storage andprocessing circuitry 28 may be used to control the operation of device10. This processing circuitry may be based on one or moremicroprocessors, microcontrollers, digital signal processors,application specific integrated circuits, etc.

Storage and processing circuitry 28 may be used to run software ondevice 10, such as internet browsing applications,voice-over-internet-protocol (VOIP) telephone call applications, emailapplications, media playback applications, operating system functions,functions related to communications band selection duringradio-frequency transmission and reception operations, etc. To supportinteractions with external equipment, storage and processing circuitry28 may be used in implementing communications protocols. Communicationsprotocols that may be implemented using storage and processing circuitry28 include internet protocols, wireless local area network protocols(e.g., IEEE 802.11 protocols—sometimes referred to as WiFi®), protocolsfor other short-range wireless communications links such as theBluetooth® protocol, cellular telephone protocols, MIMO (multiple inputmultiple output) protocols, antenna diversity protocols, etc. Wirelesscommunications operations such as communications band selectionoperations may be controlled using software stored and running on device10 (i.e., stored and running on storage and processing circuitry 28and/or input-output circuitry 30).

Input-output circuitry 30 may include input-output devices 32.Input-output devices 32 may be used to allow data to be supplied todevice 10 and to allow data to be provided from device 10 to externaldevices. Input-output devices 32 may include user interface devices,data port devices, and other input-output components. For example,input-output devices may include touch screens, displays without touchsensor capabilities, buttons, joysticks, click wheels, scrolling wheels,touch pads, key pads, keyboards, microphones, cameras, buttons,speakers, status indicators, light sources, audio jacks and other audioport components, digital data port devices, light sensors, motionsensors (accelerometers), capacitance sensors, proximity sensors, etc.

Input-output circuitry 30 may include wireless communications circuitry34 for communicating wirelessly with external equipment. Wirelesscommunications circuitry 34 may include radio-frequency (RF) transceivercircuitry formed from one or more integrated circuits, power amplifiercircuitry, low-noise input amplifiers, passive RF components, one ormore antennas, transmission lines, and other circuitry for handling RFwireless signals. Wireless signals can also be sent using light (e.g.,using infrared communications).

Wireless communications circuitry 34 may include radio-frequencytransceiver circuitry 90 for handling various radio-frequencycommunications bands. For example, circuitry 34 may include transceivercircuitry 36, 38, and 42. Transceiver circuitry 36 may handle 2.4 GHzand 5 GHz bands for WiFi® (IEEE 802.11) communications and may handlethe 2.4 GHz Bluetooth® communications band. Circuitry 34 may usecellular telephone transceiver circuitry 38 for handling wirelesscommunications in cellular telephone bands such as at 850 MHz, 900 MHz,1800 MHz, 1900 MHz, and 2100 MHz and/or the LTE bands and other bands(as examples). Circuitry 38 may handle voice data and non-voice data.

Wireless communications circuitry 34 may include global positioningsystem (GPS) receiver equipment such as GPS receiver circuitry 42 forreceiving GPS signals at 1575 MHz or for handling other satellitepositioning data. In WiFi® and Bluetooth® links and other short-rangewireless links, wireless signals are typically used to convey data overtens or hundreds of feet. In cellular telephone links and otherlong-range links, wireless signals are typically used to convey dataover thousands of feet or miles.

Wireless communications circuitry 34 may include one or more antennas40. Antennas 40 may be formed using any suitable antenna types. Forexample, antennas 40 may include antennas with resonating elements thatare formed from loop antenna structure, patch antenna structures,inverted-F antenna structures, slot antenna structures, planarinverted-F antenna structures, helical antenna structures, hybrids ofthese designs, etc. Different types of antennas may be used fordifferent bands and combinations of bands. For example, one type ofantenna may be used in forming a local wireless link antenna and anothertype of antenna may be used in forming a remote wireless link antenna.

Antenna diversity schemes may be implemented in which multiple redundantantennas are used in handling communications for a particular band orbands. In an antenna diversity scheme, storage and processing circuitry28 may select which antenna to use in real time based on signal strengthmeasurements or other data. In multiple-input-multiple-output (MIMO)schemes, multiple antennas may be used to transmit and receive multipledata streams, thereby enhancing data throughput.

Illustrative locations in which antennas 40 may be formed in device 10are shown in FIG. 2. As shown in FIG. 2, electronic device 10 may have ahousing such as housing 12. Housing 12 may include plastic walls, metalhousing structures, structures formed from carbon-fiber materials orother composites, glass, ceramics, or other suitable materials. Housing12 may be formed using a single piece of material (e.g., using a unibodyconfiguration) or may be formed from a frame, housing walls, and otherindividual parts that are assembled to form a completed housingstructure. The components of device 10 that are shown in FIG. 1 may bemounted within housing 12. Antenna structures 40 may be mounted withinhousing 12 and may, if desired, be formed using parts of housing 12. Forexample, housing 12 may include metal housing sidewalls, peripheralconductive members such as band-shaped members (with or withoutdielectric gaps), conductive bezels, and other conductive structuresthat may be used in forming antenna structures 40.

As shown in FIG. 2, antenna structures 40 may be coupled to transceivercircuitry 90 by paths such as paths 45. Paths 45 may includetransmission line structures such as coaxial cables, microstriptransmission lines, stripline transmission lines, etc. Paths 45 may alsoinclude impedance matching circuitry, filter circuitry, and switchingcircuitry. Impedance matching circuitry may be used to ensure thatantennas 40 are efficiently coupled to transceiver circuitry 90 incommunications bands of interest. Filter circuitry may be used toimplement frequency-based multiplexing circuits such as diplexers andtriplexers. Switching circuitry may be used to selectively coupleantennas 40 to desired ports of transceiver circuitry 90. For example,in one operating mode a switch may be configured to route one of paths45 to a given antenna and in another operating mode the switch may beconfigured to route a different one of paths 45 to the given antenna.The use of switching circuitry between transceiver circuitry 90 andantennas 40 allows device 10 to support multiple communications bands ofinterest with a limited number of antennas.

In a device such as a cellular telephone that has an elongatedrectangular outline, it may be desirable to place antennas 40 at one orboth ends of the device. As shown in FIG. 2, for example, some ofantennas 40 may be placed in upper end region 42 of housing 12 and someof antennas 40 may be placed in lower end region 44 of housing 12. Theantenna structures in device 10 may include a single antenna in region42, a single antenna in region 44, multiple antennas in region 42,multiple antennas in region 44, or may include one or more antennaslocated elsewhere in housing 12.

Antenna structures 40 may be formed within some or all of regions suchas regions 42 and 44. For example, an antenna such as antenna 40T-1 maybe located within region 42-1 or an antenna such as antenna 40T-2 may beformed that fills some or all of region 42-1. An antenna such as antenna40B-1 may fill some or all of region 44-2 or an antenna such as antenna40B-2 may be formed in region 44-1. These types of arrangements need notbe mutually exclusive. For example, region 44 may contain a firstantenna such as antenna 40B-1 and a second antenna such as antenna40B-2.

Transceiver circuitry 90 may contain transmitters such as transmitters48 and receivers such as receivers 50. Transmitters 48 and receivers 50may be implemented using one or more integrated circuits (e.g., cellulartelephone communications circuits, wireless local area networkcommunications circuits, circuits for Bluetooth® communications,circuits for receiving satellite navigation system signals, poweramplifier circuits for increasing transmitted signal power, low noiseamplifier circuits for increasing signal power in received signals,other suitable wireless communications circuits, and combinations ofthese circuits).

Device 10 may be a relatively large device (e.g. the lateral dimensionsof housing 12 may be tens of centimeters or larger) or may be arelatively compact device such as a handheld device that has alongitudinal dimension along the main axis of housing 12 that is 15 cmor less, 10 cm or less, or 5 cm or less, and that has smaller transversedimensions. In miniature devices such as wrist-mounted, pendant, andclip-mounted devices, the dimensions of housing 12 may be 10 cm or lessor 5 cm or less (as examples).

Particularly in housings for device 10 that are compact, it may bedifficult or impossible to widely separate various antennas from eachother. For example, some antennas (e.g., antennas 40T-1 and 40T-2 in theexample of FIG. 2) may be located adjacent to each other within housing12. Other antennas (e.g., the antenna structures of region 42 and theantenna structures of region 44) may be separated only by the relativelymodest length of device 10.

Due to the close proximity of the antennas within device 10 in at leastsome device configurations, there may be a potential for interferencebetween bands. This potential for interference may be exacerbated by thepresence of the circuitry in paths 45, which may generate undesirablefrequency harmonics. For example, switches in paths 45 may havenon-linear properties that lead to the generation of second harmonics,third harmonics, and higher-order harmonics when passing radio-frequencysignals.

During data transmission operations, radio-frequency signals that aregenerated by transceiver 90 may are transmitted through paths 45 toantennas 40. Transmitted signals may, for example, be generated at afrequency f at one of the ports associated with transceiver 90.Frequency f may be associated with a cellular telephone band or otherfrequency of interest. Paths 45 may contain a switch such as atransistor-based switch. As the signals at frequency f pass through theswitch (and other non-linear circuit elements in paths 45), frequencyharmonics may be generated at frequencies such as 2f, 3f, 4f, andhigher. In this situation, a signal harmonic at 2f, 3f, 4f, or highermight be transmitted from one antenna (e.g., a cellular telephoneantenna) at the same time that signals at frequency f are beingtransmitted. The frequency harmonics at 2f, 3f, and 4f might then bereceived by another antenna in the device (e.g., a wireless local areanetwork antenna or satellite navigation antenna). If care is not taken,the received signals at harmonic frequencies of frequency f may causeundesirable interference. For example, a received signal at 2f, 3f, or4f might fall within or near a communications band of one of receivers50 (e.g., a wireless local area network receiver or satellite navigationsystem receiver). Left uncorrected, the presence of this type ofinterference may prevent satisfactory simultaneous operation of thetransmitter at frequency f and the receiver operating at 2f, 3f, 4f, orother harmonic.

Device 10 can reduce or eliminate this type of undesirable interferenceby including filtering circuitry in paths 45 that blocks harmonicsassociated with transmitted signals before they reach antennas 40.Because the magnitude of transmitted harmonics is substantially reduced,the magnitude of any harmonics that are received by other antenna andreceiver circuitry in device 10 is substantially reduced. By effectivelypreventing harmonics from being transmitted, the potential for signalinterference is eliminated and satisfactory device operation is ensured.

The filtering circuitry may include a diplexer filter that is used tomultiplex low band and high band transmitted signals onto a commontransmit path. During signal reception operations, the diplexerdemultiplexes received signals based on their frequency. The diplexermay include a low pass filter that is coupled to low band transceiverports through a low band switch. The diplexer may also include a highpass filter or a bandpass filter that is coupled to high bandtransceiver ports through a high band switch.

Even if harmonics are generated in the switches, the harmonics will beblocked by the filtering circuitry of the diplexer. For example,consider a low band frequency such as frequency f. As a signal at thisfrequency passes through the low band switch, harmonic signals at 2f,3f, and 4f may be generated. By proper configuration of the cutofffrequency of the low pass filter, signal frequency f will fall withinthe pass band of the low pass filter, but signal frequencies 2f, 3f, and4f will fall outside of the pass band and will be attenuated. Becausethe low pass filter blocks undesired harmonic frequencies, receivers 50in device 10 that operate at or near harmonic frequencies (e.g., 2f, 3f,4f, and higher) will not be subject to harmonic interference and canoperate at the same time as the transmitter operating at frequency f.Frequency harmonics generated when transmitting signals from the highband transceiver through the high band switch can likewise be attenuatedby the high-frequency attenuation properties of the high-band filter(i.e., when the high-band filter is implemented using a bandpass filterthat passes desired high-band frequencies while attenuating harmonics ofthese desired high-band frequencies).

A filtering arrangement based on a diplexer scheme of this type mayexhibit lower insertion loss than filtering arrangements based oncomponents with higher insertion losses such as notch filters. Ifdesired, additional filtering circuitry may be used in device 10. Ingeneral, the filtering circuitry in paths 45 may, include diplexers,triplexers, notch filters, bandpass filters, low pass filters, high passfilters, other filter components, and combinations of filter circuitssuch as these. Filtering components may, for example, be implementedusing surface acoustic wave (SAW) or bulk acoustic wave (BAW) devices.

An illustrative configuration that may be used for wirelesscommunications circuitry 34 is shown in FIG. 3. As shown in FIG. 3,device 10 may include antennas 40 in housing 12. Antennas 40 may becoupled to transceiver circuitry 38 and 46 using paths 45. Paths 45 mayinclude switching circuitry 64.

Antennas 40 may include one or more antennas. One or more antennas 40may, for example, be used for cellular telephone communications bands,one or more antennas 40 may be used for satellite navigation systembands such as the GPS band at 1575 MHz, and one or more antennas 40 maybe used for other communications bands of interest (e.g. the IEEE 802.11bands at 2.4 GHz and 5 GHz or other wireless local area network bands,the Bluetooth® band at 2.4 GHz, etc.). In a configuration of the typeshown in the example of FIG. 3, one or more antennas such as antenna 40Amay be associated with wireless transceiver circuitry such as remotewireless transceiver circuitry 38 (e.g., one or more cellular telephonetransceiver circuits) and one or more antennas such as antenna 40B maybe associated with wireless transceiver circuitry 46 (e.g., satellitenavigation system receiver 42 of FIG. 1, local wireless transceivercircuits 36 of FIG. 1 such as IEEE 802.11 wireless local area networkcircuits, Bluetooth® circuits, etc.). Additional antennas may beassociated with transceiver circuitry 38 (i.e., antennas in addition toantenna 40A) and additional antennas may be associated with transceivercircuitry 46 (i.e., antennas in addition to antenna 40B), if desired.

Transceiver circuitry 38 may include transmitters 48 and receivers 50.There may be, for example, a respective transmitter 48 and a respectivereceiver 50 associated with each of a plurality of cellular telephonecommunications bands. Consider, as an example, LTE Band 13. To supportcommunications in E-UTRA (LTE) Band 13, one of transmitters 48 (e.g.,transmitter TX of FIG. 3) may transmit radio-frequency signals in theuplink frequency range of 777 MHz to 787 MHz and one of receivers 50(e.g., receiver RX of FIG. 3) may receive radio-frequency signals in thedownlink frequency range of 746 MHz to 756 MHz. To increase transmitpower before transmitted radio-frequency signals reach antennas 40,paths 45 may include power amplifiers such as power amplifier 52. Toincrease the strength of signals that have been received from antennas40, paths 45 may include low noise amplifiers (LNAs) such as low noiseamplifier 60. Amplifiers such as amplifiers 52 and 60 may be implementedusing discrete components, using circuitry that is part of a transceiverintegrated circuit, etc.

Switching circuitry 64 may include multiple switches each of which isassociated with a respective frequency range. In the example of FIG. 3,switching circuitry 64 includes first switch 64LB and second switch64HB. The states of switches 64LB and 64HB (i.e., which terminals areconnected to each other in the switches) may be controlled by usingstorage and processing circuitry 28 to apply control signals to controlterminals 62. Switch 64LB may be used to handle radio-frequency signalswith lower frequencies than switch 64HB. With this type of arrangement,switch 64LB may sometimes be referred to as a low band switch and switch64HB may sometimes be referred to as a high band switch.

Switches 64LB and 64HB preferably have a sufficient number of terminals(switch ports) to allow all desired transmitters 48 and receivers 50 tobe coupled to antennas 40. In a typical configuration, switches 64LB and64HB may be SPOT (single pole four throw) or SP5T (single pole fivethrow) switches (as an example). Switches with more terminals or fewerterminals may be used if desired.

Each switch has one terminal T′ that is coupled to diplexer 68 and aplurality of other terminals T that are each coupled to a respectiveportion of transceiver circuitry 38. In a typical configuration, eachtransmitter and receiver pair in transceiver circuitry 38 is coupled toa respective terminal T in switch 64LB or 64HB using a component such asdiplexer 54. With this type of arrangement, transmit and receive signalsfor each band of interest are associated with a respective switchterminal T.

In the example of FIG. 3, low band switch 64LB has a plurality ofterminals T each of which is coupled to a respective transmitter 48 andreceiver 50 by a respective path 66 and associated filter circuitry suchas diplexer 54. For example, transmitter TX may be connected to filter56 in diplexer 54 and receiver RX may be connected to filter 58 indiplexer 54. Filter 56 may be a high pass filter that passes signals inthe uplink range of Band 13 and filter 58 may be a low pass filter thatpasses signals in the downlink range of Band 13.

Diplexer 54 may be coupled to a given one of terminals T in low bandswitch 64LB by one of paths 66. Transmitted signals from transmitter TXin the uplink frequency range for Band 13 may be routed to the giventerminal T by power amplifier 52 and filter 56 of diplexer 54. Receivedsignals in the downlink frequency range for Band 13 may be routed fromthe given terminal T to receiver RX by filter 58 and low noise amplifier60. Other bands (e.g., other LTE bands, GSM bands, etc.) may be handledusing their own respective transmitters 48, power amplifiers 52,receivers 50, low noise amplifiers 60, and diplexers 54.

The transceiver circuitry for a first set of the frequency bands handledby transceiver circuitry 38 (e.g., the lower frequency bands) may becoupled to the terminals T of low band switch 64LB. The transceivercircuitry for a second set of the frequency bands handled by transceivercircuitry 38 (e.g., the higher frequency bands) may be coupled to theterminals T of high band switch 64HB. With one suitable arrangement,frequencies below about 960 MHz may be handled by low band switch 64LBand frequencies above about 1710 MHz may be handled by high band switch64HB. Other configurations may be used in wireless circuitry 34 ifdesired. These frequency assignments are merely illustrative.

Diplexer 68 may have filters FLB and FHB and ports (terminals) PL, PH,and PA. Terminal T′ of switch 64LB may be coupled to port PL. TerminalT′ of switch 64HB may be coupled to port PH. Port PA of diplexer 68 maybe coupled to antenna 40A. Filter FLB may be a low pass filter. FilterFHB may be a high pass filter or a bandpass filter. Diplexer 68 may usefilters FLB and FHB to route radio-frequency signals between switchingcircuitry 64 and antenna 40A according to frequency, while blockingundesired signal harmonics.

FIG. 4 is a graph showing an illustrative radio-frequency signaltransmission characteristic that may be associated with filter FLB. Asshown in FIG. 4, filter FLB may be a low pass filter that passes signalswith frequencies f below frequency f1. The value of f1 may be, forexample, 960 MHz or other frequency that is above the frequenciesf_(LB1) . . . f_(LBN) of the communications bands that are beingtransmitted and received via switch 64LB. Using low pass filter FLB,diplexer 68 may exhibit an insertion loss of about 0.3 dB between portsPL and PA (i.e., maximum transmission value T2 of filter FLB may beabout 0.3 dB below 100% transmission level T1, as indicated by the gapbetween 100% transmission curve 70 and transmission curve 72 of filterFLB.

FIG. 5 is a graph showing an illustrative radio-frequency signaltransmission characteristic that may be associated with filter FHB. Asshown in FIG. 5, filter FLB may be a high pass filter (see, e.g., curve76 and curve portion 80-2) or a bandpass filter (see, e.g., curve 76 andcurve portion 80-1) that passes signals with frequencies f abovefrequency f2. The value of f2 may be, for example, 1710 MHz or otherfrequency that is below the frequencies f_(HB1) . . . f_(HBN) of thecommunications bands that are being transmitted and received via switch64HB. Using high pass filter (or bandpass filter) FLB, diplexer 68 mayexhibit an insertion loss of about 0.3 dB between ports PH and PA. Asshown in FIG. 5, for example, the maximum transmission value T2 offilter FHB may be about 0.3 dB below 100% transmission level T1, asindicated by the gap between 100% transmission curve 70 and transmissioncurve 76 of filter FHB (diplexer 68). The insertion losses associatedwith diplexer 68 may be somewhat higher or lower than the illustrative0.3 dB insertion loss shown in FIGS. 4 and 5. Nevertheless, theinsertion losses associated with use of a diplexer such as diplexer 68will generally be significantly less than the insertion losses thatwould result if other types of filtering circuitry such as notch filterswere to be interposed between switching circuitry 64 and antenna 40A.

Switching circuitry 64 may be implemented using switches 64A and 64Bthat include gallium arsenide field-effect transistors (FETs),microelectromechanical systems (MEMS) switches,metal-oxide-semiconductor field-effect transistors (MOSFETs), p-i-ndiodes, high-electron mobility transistors (HEMTs), pseudomorphic HEMT(PHEMTs), transistors formed on a silicon-on-insulator (SOI) substrate,etc. When radio-frequency signals are transmitted from transmitters 48to antenna 40A, the transmitted signals pass through switching circuitry64. Nonlinearities in the behavior of switching circuitry 64 maygenerate harmonics at terminals T′ (i.e., at the outputs of theswitches). The filters of diplexer 68 can significantly attenuate theseharmonics, so that the harmonics are not transmitted through antenna 40Aand are therefore not received by antenna 40B. Because antenna 40B doesnot receive harmonics of any significant magnitude, the receiversassociated with transceiver 46 (i.e., wireless local area networkreceiver circuitry, satellite navigation receiver circuitry, etc.) willoperate properly without interference from the operation of transceivercircuitry 38.

Consider, as an example, a situation in which the communications bandsthat pass through low band switch 64LB and low pass filter FLB (i.e.,bands 74 at frequencies f_(LB1) . . . f_(LBN) of FIG. 4) are associatedwith LTE bands such as some or all of Bands 5, 8, 17, 13, and 20 (and,if desired, other LTE bands and/or other cellular telephone bands),whereas the communications bands that pass through high band switch 64HBand high pass filter (or bandpass filter) HLB (i.e., bands 78 atfrequencies f_(HB1) . . . f_(HBN) of FIG. 5) are associated with LTEbands such as some or all of Bands 4, 2, 7, 1, 3, and 40 (and, ifdesired, other LTE bands and/or other cellular telephone bands). In aconfiguration of this type, harmonics of some of the transmitted LTEbands may fall within IEEE 802.11 (WiFi®) bands at 2.4 GHz and 5 GHzand/or satellite navigation system bands such as the GPS band at 1575MHz. For example, the uplink (transmit) band associated with Band 13extends from 777 MHz to 787 MHz. When Band 13 traffic is transmitted bytransceiver circuitry (e.g., transmitter TX of FIG. 3), switch 64LB maygenerate harmonics such as second harmonics in the frequency range of1554 MHz to 1574 MHz. If not attenuated by diplexer 68, these secondharmonics (particularly the harmonic signals near 1574 MHz) mightinterfere with the GPS band centered at 1575 MHz (i.e., the GPS receivercoupled to antenna 40A). By using diplexer 68, however, the secondharmonics in the frequency range of 1554 MHz to 1574 MHz are attenuatedsignificantly (e.g., by 15 dB or more, by 30 dB or more, etc.). As shownin FIG. 4, for example, low pass filter FLB significantly attenuatessignals at frequencies above f1 (e.g., above 960 MHz or other suitablecutoff frequency).

The third harmonics of LTE bands 1, 3, 4, and 2 may represent a possiblesource of interference with the IEEE 802.11 wireless local area networkband at 5 GHz. When signals in these LTE bands are transmitted throughswitch 64HB, third harmonics in the vicinity of 5 GHz may be produced.As indicated by curve 76 and, in particular, curve segment 80-1 of FIG.5, when filter FHB is implemented as a bandpass filter (i.e., whenfilter FHB passes signals in a frequency range f2 to f3 of about 1710MHz to 2.25 GHz), signals above 2.25 GHz (i.e., the harmonics in thevicinity of 5 GHz) will be attenuated by filter FHB. As with the secondharmonics of Band 13 that are attenuated by filter FLB, these harmonicswill not reach antenna 40B. Because diplexer 68 prevents transmittedsignal harmonics from being transmitted through antenna 40B, theseharmonics will not be received by antenna 40A, even when antennas 40Aand 40B are located within the same device (e.g., at ends 44 and 42,respectively) and are potentially in close proximity to each other(e.g., 15 cm or less apart, etc.).

If desired, the lower cutoff frequency f2 and upper cutoff frequency f3of high band filter FHB may be lower or higher to accommodate differenttransmitted bands. If no receiver is used in device 10 at 5 GHz, filterFHB may be implemented using a high pass filter (i.e., filter with a lowfrequency cutoff such as frequency f2 of FIG. 5, but no sharp upperfrequency cutoff such as frequency f3 so that curve 76 follows segment80-2 above f3). Low band filter FLB can be implemented using differentcutoff frequencies. The use of a 960 MHz cutoff frequency for frequencyf1 of FIG. 1 is presented as an example.

The foregoing is merely illustrative of the principles of this inventionand various modifications can be made by those skilled in the artwithout departing from the scope and spirit of the invention. Theforegoing embodiments may be implemented individually or in anycombination.

What is claimed is:
 1. Wireless circuitry, comprising: a first set ofradio-frequency transmitters that operate in a first set ofcommunications bands, wherein the first set of radio-frequencytransmitters includes a Long Term Evolution (LTE) cellular telephonetransmitter; a second set of radio-frequency transmitters that operatein a second set of communications bands; a first switch having aplurality of first switch terminals each of which is coupled to arespective one of the radio-frequency transmitters in the first set ofradio-frequency transmitters and having an additional terminal to whicha selected one of the plurality of first switch terminals is connected;a second switch having a plurality of second switch terminals each ofwhich is coupled to a respective one of the radio-frequency transmittersin the second set of radio-frequency transmitters and having anadditional terminal to which a selected one of the plurality of secondswitch terminals is connected; an antenna; and a diplexer having a firstport that is coupled to the additional terminal of the first switch, asecond port that is coupled to the additional terminal of the secondswitch, and a third port that is coupled to the antenna.
 2. The wirelesscircuitry defined in claim 1 wherein the Long Term Evolution (LTE)cellular telephone transmitter operates in LTE Band
 13. 3. The wirelesscircuitry defined in claim 1 wherein the diplexer includes a low passfilter and a high pass filter.
 4. The wireless circuitry defined inclaim 3 wherein the Long Term Evolution (LTE) cellular telephonetransmitter operates in LTE Band 13 and produces transmitted signals atfrequency f and wherein the low pass filter prevents signals at 2f fromreaching the antenna.
 5. The wireless circuitry defined in claim 3wherein the first set of radio-frequency transmitters includes acellular telephone transmitter that produces transmitted signals atfrequency f and wherein the low pass filter prevents signals at 2f fromreaching the antenna.
 6. The wireless circuitry defined in claim 1wherein the diplexer includes a low pass filter and a bandpass filter.7. The wireless circuitry defined in claim 6 wherein the second set ofradio-frequency transmitters includes an additional Long Term Evolution(LTE) cellular telephone transmitter operating in an LTE Band selectedfrom the group of bands consisting of: Band 1, Band 3, Band 4, and Band2, wherein the additional LTE cellular telephone transmitter producestransmitted signals at a frequency f, and wherein the bandpass filterprevents signals at a frequency of 3f from reaching the antenna.
 8. Thewireless circuitry defined in claim 7 wherein the LTE cellular telephonetransmitter in the first set of radio-frequency transmitters operates inLTE Band 13 and produces signals in LTE Band 13 and wherein the low passfilter prevents signals at a second harmonic of the signals in LTE Band13 from reaching the antenna.
 9. The wireless circuitry defined in claim1 further comprising: a first set of radio-frequency receivers, whereineach of the radio-frequency receivers in the first set ofradio-frequency receivers is coupled, together with a respective one ofthe radio-frequency transmitters in the first set of radio-frequencytransmitters, to a respective one of the first switch terminals in thefirst switch; and a second set of radio-frequency receivers, whereineach of the radio-frequency receivers in the second set ofradio-frequency receivers is coupled, together with a respective one ofthe radio-frequency transmitters in the second set of radio-frequencytransmitters, to a respective one of the second switch terminals in thesecond switch.
 10. An electronic device, comprising: a first antenna; areceiver that receives signals in at least a first communications bandthrough the first antenna; a second antenna; a plurality of pairs ofradio-frequency receivers and transmitters, wherein a given one of thetransmitters transmits signals at a frequency f through the secondantenna; a diplexer having a first port, a second port, and a third portthat is coupled to the second antenna; a first radio-frequency switchthat is coupled to the first port; and a second radio-frequency switchthat is coupled between the plurality of pairs of the radio-frequencyreceivers and transmitters and the second port, wherein the diplexerprevents signals at harmonics of the frequency f from reaching thesecond antenna and from reaching the receiver through the first antennaand wherein the second radio-frequency switch has a plurality of switchterminals each of which is coupled to a respective pair of the pairs ofthe radio-frequency receivers and transmitters and has an additionalterminal coupled to the second port and to which a selected one of theplurality of switch terminals is coupled.
 11. The electronic devicedefined in claim 10 wherein the receiver is configured to receive GlobalPositioning System signals at 1575 MHz and wherein the diplexercomprises a low-pass filter that prevents signals at a frequency of 2fthat are produced in the second radio-frequency switch in response tothe transmission of the signals at the frequency f from theradio-frequency transmitter from reaching the second antenna.
 12. Theelectronic device defined in claim 10 wherein the receiver is configuredto receive IEEE 802.11 signals at 5 GHz and wherein the diplexercomprises a bandpass filter that prevents signals at a frequency of 3fthat are produced in the second radio-frequency switch in response tothe transmission of the signals at the frequency f from theradio-frequency transmitter from reaching the second antenna.
 13. Theelectronic device defined in claim 10 wherein the diplexer includes alow pass filter and a high pass filter.
 14. The electronic devicedefined in claim 10 wherein the diplexer includes a low pass filter anda bandpass filter.
 15. The electronic device defined in claim 14 whereinthe radio-frequency transmitter comprises a cellular telephonetransmitter that produces transmitted signals at frequency f and whereinthe low pass filter prevents signals at 2f from reaching the antenna.16. The electronic device defined in claim 10 wherein the receivercomprises satellite receiver circuitry that receives satellitenavigation signals through the first antenna.
 17. The electronic devicedefined in claim 10 wherein the radio-frequency transmitter comprises aLong Term Evolution (LTE) cellular telephone transmitter operating inLTE Band
 13. 18. Wireless circuitry, comprising: a set ofradio-frequency transmitters that operate in a set of communicationsbands; a switch having a plurality of switch terminals each of which iscoupled to a respective one of the radio-frequency transmitters in theset of radio-frequency transmitters and having an additional terminal towhich a selected one of the plurality of switch terminals is connected;an antenna; a diplexer having a first port that is coupled to theadditional terminal of the switch, a second port, and a third port thatis coupled to the antenna; satellite receiver circuitry that receivessatellite navigation signals through the antenna, wherein the set ofradio-frequency transmitters comprises a first set of radio-frequencytransmitters and wherein the set of communications bands comprises afirst set of communications band; a second set of radio-frequencytransmitters that operate in a second set of communications bands,wherein the switch comprises a first switch; and a second switch havinga plurality of switch terminals each of which is coupled to a respectiveone of the radio-frequency transmitters in the second set ofradio-frequency transmitters and having an additional terminal to whicha selected one of the plurality of second switch terminals is connected,wherein the second port of the diplexer is coupled to the additionalterminal of the second switch.